Sacro-anterior haemangiopericytoma: a case report

Haemangiopericytoma (HPC) is a rare vascular tumor with borderline malignancy, considerable histological variability, and unpredictable clinical and biological behavior. HPC can present a diagnostic challenge because of its indeterminate clinical, radiological, and pathological features. HPC generally presents in adulthood and is equally frequent in both sexes. HPC can arise in any site in the body as a slowly growing and painless mass. The precise cell type origin of HPC is uncertain. One third of HPCs occur in the head and neck areas. Exceptional cases of hemangioblastoma arising outside the head and neck areas have been reported, but little is known about their clinicopathologic and immunohistochemical features. This study reports on a case of a large sacro-anterior HPC in a 65-year-old male.


Introduction
Haemangiopericytoma (HPC) is an extraordinarily rare soft tissue tumor. HPC originates from the pericytes of blood vessels, which is a specific cell type that surrounds the capillary vessels. Therefore, HPC can occur in areas where capillaries are found. HPC was first named and described in 1942 by Stout and Murray 1,2 . The most frequent locations of HPC are the extremities, pelvis, retroperitoneum, head, neck, and meninges. HPCs are usually deeply located within the muscle tissue, but dermal and subcutaneous masses have also been described 3 . According to the literature, approximately one-third of all HPCs occur in the head and neck 4 . No HPC cases were found in the sacro-anterior. The pathogenesis of HPC is unclear and its clinical features are non-specific and vary according to the location of the tumor 5 . The incidence of HPC is highest among individuals aged 50 to 60 years old. The diagnosis of HPC depends on histopathologic and immunohistochemistry (IHC) findings. HPC can be classified as benign, borderline, and malignant depending on its histopathologic and clinical features 6,7 . Not all HPCs are typical; some cases of HPC present overlapping features with other vascular and mesenchymal tumors. IHC helps in excluding other differential diagnoses, but some cases with unusual findings can pose a challenge to general pathologists 3 .
After the tumor was excised, the patient reported no pain or discomfort. Hence, he refused chemoradiotherapy. Ten months later, the patient felt abdominal pain. The patient then went to the hospital and underwent color Doppler ultrasound of the pelvic cavity. The ultrasound results revealed that the HPC recurred, resulting in the patient receiving radical surgical excision again. The pathology and IHC certified that the excised tumor was a recurred HPC. However, the patient still refused chemoradiotherapy. One month later, the patient suffered from frequent coughing and then underwent a chest CT scan. The chest CT scan revealed that the tumor had metastasized into the right lung. The larger metastatic tumor is located in the middle and lower lobe of the anterior basal segment. The tumor was approximately 1.8 cm × 1.1 cm and had a smooth morphology. The smaller tumor was approximately 0.5 cm × 0.6 cm (Figure 3). The patient accepted five cycles of EP (VP-16 + DDP) chemotherapy and metastases radiotherapy. After chemoradiotherapy, the patient's condition improved. Six months later, the patient had no complaints and the CT scan showed no evidence of recurrence (Figure 4). The study was approved by the institutional ethics committee.

Discussion
W hile the classification scheme of the World Health Organization (WHO) for CNS neoplasms considers SFT and HPC as distinct entities with different prognostic implications 8 , SFT and HPC are considered variants of a single entity, with the term "HPC" considered as obsolete 8 . Recent detection of NAB2-STAT6 fusions in both SFT and HPC has provided further support to the notion of a single pathologic entity 9,10 .
HPC is a rare vascular tumor that originates from the pericytes of blood vessels that are also called Zimmurman cells 11 . The Zimmurman cell is a discontinuous spindle cell, which adheres to the reticular fiber membrane. The Zimmurman cell is a juvenile mesenchymal cell that facilitates contraction and potential secretion and can transfer to HPC under pathologic     16 . Imaging examinations can only judge the size and boundary of the tumor. Previous studies reported that HPCs observed by CT generally appear as wellcircumscribed masses, which are dramatically enhanced after injection of contrast material; meanwhile in MRI images, HPCs are highly intense in T1 and slightly intense in T2 3 . The general morphology of the tumor is round to oval-shaped, and the size of the tumor ranges from 5 to 15 cm 17 , with or without diolame 18 . HPC has no pathognomonic clinical or radiological signs. Therefore, diagnosis can only be made after careful histopathological examination. The diagnosis of HPC is often made after excluding other tumors that demonstrate HPClike features. The histologic characteristics of HPC are the tumors that have rich capillary networks and closely arranged tumor cells in the peripheral blood vessels. Tumor cells are intensive skin cells that may be round, oval, or fusiform with unclear boundaries 5,6 . The relative characteristics of HPC immunohistochemically are CD34, Vimentin, CD99, and BCL-2 positive and negative Actim and Desmin 19 . The prediction of the clinical behavior of HPC does not always correlate with the histolopathologic features of the tumor. The strict universal histopathologic criteria for malignancy have not been made. The existing malignancy criteria for HPC vary between different studies. The most common metastases sites of HPC are the lungs, mediastinum, liver, and bone. Unfortunately, the aggressive behavior of HPC is unpredictable because benign tumors can become malignant and metastasize 20 . Generally, the large size (>5 cm), increased mitotic rate (>4 mitosis/10 H PF), presence of atypical mitosis, high cellularity, pleomorphic tumor cells, and foci of hemorrhage and necrosis predict a highly malignant course 7,13-15 . A tumor that has a size larger than 2.0 cm and located in a deep site (in the absence of nuclear atypia) demonstrates uncertain malignant potential 20 .
The histopathology of HPCs has been well-documented, but the fine-needle aspiration biopsy (FNAB) results are rarely described [21][22][23][24] . FNAB is difficult to use in the diagnosis of primary HPC. However, cytologic analysis may diagnose the recurrence or metastasis of HPC 23 . Incisional biopsy for tumors is not advised because the tumor is considered to be vascular, and the risk of bleeding and consequent fibrosis is present. Furthermore, FNAB is not used in HPC because the primary treatment is always surgery regardless of the pre-operative cytologic findings.
Given the unexpected and potentially aggressive behavior of HPCs, complete excision is the recommended treatment. The common problem with HPC is local recurrence after incomplete excision, with rates varying from 13% to 40%. In cases of local recurrence, adjuvant radiotherapy and chemotherapy can be offered.
Although the results of adjuvant radiotherapy and chemotherapy vary, adjuvant radiotherapy and chemotherapy are still used as supplementary treatment for HPCs. HPCs are not sensitive to radiotherapy. Radiotherapy is reserved only as adjuvant therapy for cases of incompletely excised tumors, recurrent tumors, and tumors with high-grade histopathologic features. Chemotherapy may have a role in the treatment of distant metastatic disease, but its role in the primary treatment of HPC remains unclear. Vincristine, Adriamycin, and Cyclophosphamide have been used in cases of aggressive HPCs with variable success 25 . Some reports showed that the use of interferon may benefit patients with pulmonary HPC metastases 26 . Some studies reported local recurrence rates of as high as 40%, with metastatic disease in 15% of the cases reported with a latency period ranging from 63 to 107 months 27 . In our case, after operation, radiotherapy, and chemotherapy, the patient's clinical symptoms nearly completely disappeared, and the CT scan (Figure 4) revealed that the tumor did not recur.

Conclusion
HPC is a rare soft tissue tumor with high histological variability and unpredictable clinical and biological behavior. One third of HPCs occur in the head and neck and only a few cases have been reported regarding tumor localization in the sacro-anterior. Preoperative evaluation must include a thorough imaging evaluation (CT and MRI scan), including the results that may not be specific for HPCs. The treatment of choice is radical excision. HPCs are potentially malignant, regardless of the benign pathology. Given the possibility of recurrence and metastasis in HPC cases, surgical excision may not be sufficient 28 . After tumor excision, adjuvant chemotherapy is necessary. During follow-up visits, imaging examination is used to determine recurrence and metastasis.